1. Field of the Invention
The present invention relates to a display used for vehicles and more particularly to a display for indicating information such as vehicle speed to the driver, which information exists as a virtual image appearing at a distance from the driver's eyes.
2. Prior art
Many of conventional on-vehicle displays used for automotive vehicles are installed, for example, under the dashboard of the vehicle so that the displays are out of the driver's sight while the driver is driving the vehicle. While driving the vehicle, the driver's eyes move mostly in the horizontal direction since the driver is watching for oncoming traffic. However, the driver has to move his or her eyes vertically whenever the driver wishes to look at, for example, the speedometer under the dashboard. This is inconvenient particularly when the vehicle is running at relatively high speeds, and becomes increasingly inconvenient as the vehicle speed increases. One way of solving the aforementioned problem is to employ a head-up display where an image indicative of driving information is within the driver's sight while the driver is driving the vehicle. The image is viewed within the driver's sight but at a distance from the driver's eyes so that the driver needs to move his eyes only by small angles.
As shown in FIG. 6, Japanese Patent Preliminary Publication No. 60-192912 discloses an on-vehicle display for use in automotive vehicles. A projector 1 projects an image indicative of vehicle information, e.g., vehicle speed, onto a mirror 2b which in turn reflects the image to the inner surface of a windshield 3 through an opening 4a in a dashboard 4. The windshield 3 then reflects the light into the driver's eyes E1 so that the driver views a virtual image X1 at a distance behind the windshield 3. A motor 2a drives the mirror 2b to adjust inclination of the mirror 2 so that the position of the virtual image may be adjusted between position X1 and X2. However, not only the position of the virtual image is vertically moved only a little but also the image may often be out of the driver's eye range so that the driver must move his/her eyes to E2 to view the image X2. Therefore, the driver has to change his or her position in order to view the virtual images X1 and X2.
Sometimes, head-up displays are not advantageous, particularly on a fine day, in that small differences in intensity between the ambient light and the virtual image results in poor contrast of the virtual image. Moreover, the virtual image appears in the driver's sight when the vehicle is running at high speeds. This disturbs the driver's sight. The image tends to be reflected by both the outer surface and inner surface of the windshield 3 at night so that the display image may often be dual, resulting in poor display quality.